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Durum Wheat & Rye Create High Acetic Acid Content

Durum Wheat & Rye Create High Acetic Acid Content

After a series of experiments I've come to a partial conclusion that rye and durum wheat both create high acidity starters that impart the sour tang to the finished bread. Wholewheat, AP, Hard Red Winter and Spring do not produce high acidity from my refrigerated low hydration starter.

Starter conditions:

High hydration - 100% Flour 100% Water

Culture innoculant - 20% refrigerated firm starter

Fermenting Temp - 74 dF

Length of Ferment - 18/24 hours

There isn't any flour quality or type dependency other than it be rye or of duram [semolina] wheat.

I've looked at a lot of the literature and searched this site, which has now begun to show up on the front of the list on Google searches by the way, with no results. My thesis at this point is that there is a component [or components] in both rye and durum that enhance the increased acetic acid growth in the culture.

One other observation point - the levaining action seems to be suppressed by the souring requiring long periods for proofing.

The sourest bread that I have ever made or eaten was whole wheat, no rye or durum included. And by sour, I mean wincingly, puckering sour. No-fun-to-eat sour, for my tastes. This was made with the very first starter I had ever grown and I knew diddly about sourdough at the time. It was enough to put me off sourdough for another two or three years.

In retrospect, I suspect that the ratio of yeasts to bacteria in my starter was far too strongly tilted in favor of the bacteria. Consequently, by the time the dough was showing enough signs of aeration to suggest that it should be baked, the acid load was very high. Based on reading that I have done in years since, especially including Debra Wink's observations, I suspect that it has something to do with the buffering capacity of whole wheat flour, although I don't begin to profess a solid understanding of the biology or chemistry involved.

I offer this as another factor for your consideration, not as a contradiction to what you have postulated.

I've tried whole wheat starter that is then incorporated into high extraction flour dough. It comes out with a fairly faint sourdough flavor but not like that made with rye or durum flour.

Buffering action by whole wheat flour is an interesting lead though I'm hanging on to the original thesis - that rye and durum contain elements which promote acetic acid production. You're right about the bacteria count over yeast - leavaning of loaves is problematic.

Control of acetic acid production in seed starters is the goal. I've used rye to adjust sourness for years though durum as a souring agent is a fairly new phenomenon to the repetoire. I think that understanding the basics of acetic acid production [within this somewhat narrow band] would prove valuable to all SD bread bakers.

Forgive me if you're already taking this into account, but I almost always use stoneground rye for my seed starter - and levain. Yet I only get an overly sour result to the finished bread - if the seed starter or levain is highly hydrated. Hence I keep both seed (at the point where the wild yeast becomes active) and levain fairly dry - biga style. The seed starter is never more than 75% hydrated. The levain far drier still - just wet enough to be able to mould into a fairly stiff ball, nothing more. After fermenting at room temp overnight - even at 78 df temps - it still remains in a ball - very little flattening out. Yet unleashed into the main dough, once water is added, it is clear that ball was full of healthy active yeast raring to go. And the finished bread has a gentle sd tang, but not overpowering. No issues with leavening either. Despite a highly hydrated finished dough, it rises well enough and does not require extensive proofing even when retarded. I retard the shaped loaves, by the way.

But if I keep the rye wet for my maturing seed and levain - certainly at 100% hydration - it quickly goes from sweet to intensely yeasty to sour. The finished bread way too sour for my liking. And frequently a flatter, more spread finished bread. I think this aspect - using hydration to favour either the yeast or LAB - was covered in Debra's article, wasn't it? Been a long time since I read it, so make that a tentative memory shot!

...and some contradictions. My most sour breads come from starters that are minimally hydrated (say 50%) for wheat-based starters. Breads like Robertson's Tartine Country bread use 125% hydration starter and are minimally sour. Also, I am confused by the original premise. I thought that traditional sourdough taste comes from lactic acid rather than acetic acid, because acetic is more volatile and likely to burn off during bake.

... regarding the effect of hydration and temperature on acidification:

Acidification is also influenced by hydration and temperature. Contrary to popular belief, all three groups of sourdough lactobacilli prefer wetter doughs a bit on the warm side, many growing fastest at about 90ºF or a little higher. For the homofermentive species producing only lactic acid, increasing activity by raising the hydration and/or temperature will increase acid production. Decreasing activity by reducing hydration or by retarding will slow production. There is a direct relationship between activity and lactic acid. During heterofermentation, for each molecule of glucose consumed, one lactic acid is produced, along with one carbon dioxide (if a hexose is fermented), and either one ethanol or one acetic acid. But under wetter, warmer conditions, where sugars are metabolized more rapidly, the tendency is toward lactic acid and alcohol production in obligate heterofermenters, and all lactic acid (homofermentation) in the facultative heterofermenters. Lactic acid production is directly related to activity during heterofermentation just as in homofermentation, even if only half the rate.

At lower hydrations and temperatures (lower activity), more acetic acid is produced, but not because of temperature per se. Acetic acid production is influenced indirectly by temperature, in that it affects the kinds of sugars available. The fructose that drives acetic acid production, is liberated from fructose-containing substances in flour, largely through the enzyme activity of yeast. And, because lower temperatures are more suited to yeast growth than higher, more fructose is made available to the bacteria at lower temperatures. At the same time, the bacteria are growing and using maltose more slowly, so the demand for co-substrates goes down as the fructose supply goes up. The ratio of acetic acid to ethanol and lactic acid goes up, because a higher percentage of the maltose is being co-metabolized with fructose. Reducing hydration has a similar effect of slowing the bacteria more than yeast, which I believe is the real basis for increased acetic acid production in lean breads made with refined flours.

So lactic acid and acetic acid production respond differently to hydration levels. As an aside, I was surprised to read that - and I quote:

"And, because lower temperatures are more suited to yeast growth than higher"

Whenever I contemplate answering on a topic as expansive as this one really is, it wears me out just thinking about it, because I think a whole chapter could be written on starter maintenance and how it affects population dynamics and metabolite production. Click here for an introduction to the latter.

I wouldn't change anything that Dan said, but I will add that you will never get all lactic acid, or all acetic acid, no matter what hydration you keep your starter. All else being equal, you will get a lower percentage of the total acid as acetic, at the higher hydrations. Acetic acid will increase as a percentage of the total acid, as the hydration moves downward, but it will never be higher than lactic acid. Lactic acid will always be higher than acetic in a starter or bread dough, no matter what hydration you use.

I recently tried Hamelman's Vermont Sourdough (built on a 125% starter), because it received so many accolades here on TFL. In fact, I tried it twice, because I wasn't sure the first batch was what it should be. I may be the only one, but I didn't care for this bread at all. It was just too sour for me (and I didn't even retard it). But as you can probably guess, I am not a sour seeker. Next I tried the Pain au Levain. It is essentially the same overall formula---same dough hydration, and same percentage of pre-fermented flour. The difference is that it is built on a firm 60% starter, and has 5% rye flour instead of 10. Seemingly small changes, but what a big difference it made in the character of the bread. This one, I loved. It was mild in flavor, and had the most heavenly wheaty aroma.

So, why does my firm starter produce milder bread than my liquid one, when firm starters have a higher percentage of acetic acid? Because it has a lower total acid concentration. More specifically, the bacteria grow slower in a dry starter, so their population shrinks over multiple refreshments (yeast seem to hold their own). Because their population is smaller and they're growing slower, acid production is likewise reduced. But this brings us around to the other factors, which Dan has listed above---temperature, the size of feedings, and the length of feeding intervals. These also play a big part in population dynamics and acidity.

... refrigeration increases the acetic acid content of dough. (This does not help, of course, with Wild-Yeast's basic theory about the acetic propensities of rye and durum being greater than other flours), but it is interesting I think.

This is the extract from their (excellent) site:

What makes the sour in sourdough bread? It's a combination of lactic and acetic acids, created as the dough rises and ferments. Refrigerating the dough encourages the production of more acetic than lactic acid; and acetic acid is much the tangier of the two. Thus, sourdough that's refrigerated before baking will have a more assertive sour flavor.

It certainly fits in with my experience - though I must confess, hadn't twigged the why and how of it. I just knew I got a far milder (and for me, far more pleasing) taste, if I keep the retard phase fairly short.

After additional review, as many have suggested. it is the Acetic that is the harsher more lasting "tang" taste of sourdough though both Acetic and Lactic are present. The "Art" is finding a balance between the two that suits the bread under consideration.

Going back to the basics - with minimum equipment in a quest to bake the perfect Larraburu simile....,

I can report my own findings: adding whole rye or whole wheat in the starter intensifies the rye or wheat flavor (compared to a bread with the same formula, but the rye shifted to the main dough instead of in the starter build) and also increases the acid a small amount, though to me it seems like the acid is tied up with the whole grain flavor, I don't really notice it on its own but only as a part of the grain. It also seems to slow the yeast activity and rise in the final dough. I haven't tried semolina/durum in sourdough yet.

My thinking is that the main reason for the increased acid is the slower yeast activity, so that the bread needs a longer time to proof properly.

re: temperature- I made a bunch (twenty) of little sourdough rolls, each with different parameters of hydration or starter temperature, each on its own labelled parchment square. Each roll was 50% starter (to maximize flavor differences) and all white flour. In the end, the differences in starter hydration didn't make much difference in taste if fermentation time and temp were held constant. So I only use a liquid starter when I want a lot of protease for extensibilty in shaping (baguette, pizza). However, differences in temperature made noticeable differences in flavor, regardless of hydration. My favorite flavor came from a starter build fermented at 70-73F, which had both milky sweet notes and acid to balance them. Starters fermented at 80F were sort of tasteless.

re: more yeast acivity at higher or lower temps- it depends on the temp! In sourdough, yeast activity is maximized at 78-80F, where it's roughly equal to bacterial activity. Yeast activity drops off quickly as temps move higher than 80F. And the delicate little buggers start dying off by 90F, so temp control is important in this range. Below 78F, yeast activity drops off more quickly than bacterial activity, but not as quickly as it does above 80F. So moving away from 78-80F (in either direction) favors bacterial activity over yeast.

I ferment all my starters and starter builds as close to 70F as possible, but then ferment the main doughs at 78-80F to maximize yeast activity. Extending bulk fermentation/bench rest past 3 hours at 78F seems to me the most effective way of increasing acid. At least in my doughs, 3hrs @78F is sort of a tipping point after which I get more noticeable acid in the final bread- too much for my taste. My breads have some acid and taste like sourdough, but they are not anywhere near the realm of San Francisco-style sourdoughs. They seem to be crowd pleasers, even kids like them.

I used to enjoy feeding my starter 10% whole grain (usually rye), but stopped doing that when I realized it was slowing the rise in the final dough. I still use whole rye in starter builds for a bread, just not in the maintenace of my culture.

I wouldn't change anything that Dan said, but I will add that you will never get all lactic acid, or all acetic acid, no matter what hydration you keep your starter. All else being equal, you will get a lower percentage of the total acid as acetic, at the higher hydrations. Acetic acid will increase as a percentage of the total acid, as the hydration moves downward, but it will never be higher than lactic acid. Lactic acid will always be higher than acetic in a starter or bread dough, no matter what hydration you use.

In general, this has always been my experience, too.

My typical modus operandi is to work with 75% or 125% hydration starters. I store them in the fridge and feed them intermittently when not baking regularly. I notice that the 75% starter is always more pungent (acetic acid) than the 125% starter, but that the latter has a really good bite (lactic acid) when tasted. Leaving both out at RT, typically 70-80F in my house, leads to more acetic acid odor and alcohol after they have peaked.

I'd expect the different flours to favor different populations and strains of bacteria which would be reflected in their acidity profiles. Other factors such as enzyme natural abundances might come into play, too.

I know the conventional wisdom is that higher hydration favors lactic acid and lower hydration favors acetic acid, but my own experience with test baking has been that hydration makes very little discernable difference in taste when fermentation time and temp are held constant. I'd be interested to hear from any others who have conducted test bakes.

After a brief respite and a little in depth thought about acquiring the "tang" the inevitable near success has occurred. No I'm not ready to publish just yet but if today's bake goes in the same direction I'll start crossing the "Ts" and dotting the "Is".

By the way the original assumption regarding Durum flour as creating a more sour tasting bread was almost right. Temperature and time also play important roles - just had to climb into the way back machine and imagine bakery working conditions. Still retarding the dough for flavor development though I need to work on obtaining larger gas bubbles in the crumb.

A little progress on the "Road to Tang". It's one of those "there and back again" type stories. The quest for Larraburu style sourdough is slowly becoming a reality. "And for my next illusion" the magician said...,

These one pound loaves produced an oven spring simialr to a blimp at a mooring mast. The bottoms even rounded out with only a patch at the very bottom still touching the baking stone. A new scoring method was discovered using a razor sharp sashimi knife that makes me wonder why I hadn't thought of it before - makes scoring loaves a pleasure to perform...,

After backing into a number of blind alleys the fog of error prone indecision has cleared and, with a lot of help from all the good bakers at TFL, I am now able to bake a reasonable facsimile of bread made by the fabled Larraburu Bros. Bakery of old.

I'll be preparing the write-up over the next week or so as I'd like to get one additional bake under my belt just to insure that I'm not dreaming nor missing an important step in the process.

One item that seems to be somewhat contrary is the development of the deep acetic acid sour taste begins in the starter and then transfers to the sponge - using 50% hydration for the sponge. The sponge becomes estremely acidic as the fermentation progresses. The second, is the use of high protein flour, in this case 14% durum flour.

The hint was directly taken from the 1978 paper, "Lactic and Volatile (C2-C3) Oranic Acids of San Francisco Sourdough French Bread", by A.M. Galal et al. which detailed the preparation of Larraburu Bakery Sourdough French Bread. The other portion is that the process outlined in the afforementioned paper makes absolutely no use of low temperature retarding. In fact quite the opposite.

I've found that combining the above methodology with a retarding period produces an amazingly great bread - as pictured below...,

Those loaves look amazing and I can't wait to see what conclusions you've come to. I myself have found (though not through nearly enough trial and error) is that a high hydration starter and room temp (70 - 73 F) have given me my best sour loaf.

Thanks so much for the post, can you send me slice of those? I'm dying here!

It has taken awhile to get to this point. David Snyder's entries on SFSD bread were invaluable in this quest and I owe a debt of gratitude for his lead work on the subject. He also uses the paper on Larraburu bread as a basis for his recipe recreation.

Being able to control the sourness of the resulting bread was one of those epiphanous moments when the entire structure of the sourdough world literally fell together for me. So onward on the "Road to Tang"...,

Great looking loaves! I am always looking for a way to approximate SF SD, so I read this post top to bottom. I have not had great luck with recipes that retard (seems I can get a great result one time, and so-so the next, doing everything identical, though refrigerating is never the same), but I'm willing to try anything once.

Something that caught my eye in this thread was the quote from Debra Wink's article stating that an increase in fructose increases acetic acid production. I wonder if this is why Reinhart calls for agave syrup in just about any bread in his books with a small amount of sweetener? He never mentions this, but agave syrup does have a very high level of fructose - much more than HFCS, which is really just a bit higher than sucrose. Has anyone ever tested this, or even some pure fructose powder to SD, to see if the sour increases?

I'm off to start the bread for Easter dinner now. I won't experiment on them, but I'll definately try your bread soon, as well as something with agave (besides tequila).

Retarding is optional - the taste of bread that's been retarded is always distinctively better. I've found that you can move the retarding period around allowing changes in the process to fit a busy schedule.

I'm not familiar with the addition of agave syrup to augment acetic acid production though I trust Debra Wink's advice on the subject. Does Reinhart have Blue Agave as a sponsor?...,

Only four ingredients were used - flour, water, sea salt and starter for the experimentation. The investigation was directed toward recreating Larraburu Bros. style bread - documenting it in the form of a recipe so that it can be recreated...,

In addition to the comments above re hydration, my own experience (with rye starter)s uggests the percentage of preferment that you build up from the rye matters - 30% vs 5% will significantly increase tang factor. As does a three stage build vs. two or incorporating a long fermentation period on the sour build stage. As does a long slow rise. Many factors to consider, all are relevant to some degree. Great thread!

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